sin αst

Figure E.2: Blade coordinate system
STRUCTURAL ANALYSIS OF BLADES
The basis mesh for all analyses is created using higher-order (parabolic) tetrahedral ele-
ments. The mesh details are tabulated below:
Mesh / element property Value
Total nodes 97144
Total elements 59668
Element size 7.1 mm
Maximum aspect ratio 4.12
Elements with aspect ratio < 3 98.3%
Table E.8: Mesh details
In each analysis the mesh is refined using the adaptive h-method, which improves the
accuracy of the analysis by using more elements in critical regions. The target accuracy of
the h-method is set to 99%, which indicates intended accuracy in the convergence of the
strain energy norm. The maximum number of iterative loops is set to 5. The simulation
stops when the target accuracy is achieved or the maximum number of loops is reached.
The maximum energy norm error, which indicates the variation in strain energy at com-
mon nodes, is less than 5% for all performed analyses. The low error can be viewed to
represent similarly low stress errors in the model, which indicates a solution with a high
degree of accuracy.
Restraints
The blade is fixed as a cantilever blade by the root of the airfoil, see figure E.3. This cross-
section is considered weaker than the root of the hub junction [5, p. 69], which therefore is
left out of the model. The fixture sets all translational degrees of freedom to zero.
Figure E.3: Model restraints
153